When magma escapes from the mantle to the surface of the Earth, it causes a volcanic eruption.

Here's why:

* Magma: Molten rock found beneath the Earth's surface.

* Volcano: An opening in the Earth's crust that allows magma, ash, and gases to escape.

The pressure of the magma beneath the Earth's surface builds up. When that pressure becomes strong enough, it can overcome the strength of the surrounding rock, causing a fissure or vent to open up. This allows the magma to erupt, creating a volcanic eruption.